Methods and apparatus for an optical system outputting diffuse light and having a sensor

ABSTRACT

In some embodiments, an apparatus includes a housing and an image sensor that is coupled to the housing and has a field of view. The apparatus also includes a non-imaging optical system coupled to the housing and disposed outside of the field of view of the image sensor. The non-imaging optical system can output diffuse light in a set of directions to a surface to produce scattered light. The image sensor and the non-imaging optical system are collectively configured such that during operation, the image sensor receives at least a portion of the scattered light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/828,907, entitled “Methods and Apparatus for an Optical SystemOutputting Diffuse Light and Having a Sensor,” filed Mar. 14, 2013,which is related to U.S. patent application Ser. No. 13/828,928, nowU.S. Pat. No. 9,279,750, entitled “Methods and Apparatus for an OpticalSystem Outputting Direct Light and Having a Sensor,” filed Mar. 14,2013, the entirety of each which is incorporated by reference herein inits entirety.

BACKGROUND

The embodiments described herein relate generally to methods andapparatus for a dark field illumination system. More specifically, theembodiments described herein relate to methods and apparatus for anoptical system outputting diffuse light and having a sensor.

Pen strokes by handheld devices such as electronic pens or styluses ondisplay surfaces can be digitally recorded by optical tracking systemscontained within the handheld devices. The optical tracking systemstypically include miniaturized cameras or sensors that can digitallyrecord the pen strokes on the display surfaces. Known optical trackingsystems use opaque dots to register position with a digital pen. Thesedots are typically invisible to the naked eye but detectable by theoptical tracking system. Such known optical tracking systems typicallyuse a wide field of view to receive sufficient reflections from the dotsand have relatively low resolution.

Accordingly, a need exists for improved systems and method for theaccurate and high resolution determination of position information ofhandheld devices on display surfaces.

SUMMARY

In some embodiments, an apparatus includes a housing and an image sensorthat is coupled to the housing and that has a field of view. Theapparatus also includes a non-imaging optical system coupled to thehousing and disposed outside of the field of view of the image sensor.The non-imaging optical system can output diffuse light in a set ofdirections to a surface to produce scattered light. The image sensor andthe non-imaging optical system are collectively configured such thatduring operation, the image sensor receives at least a portion of thescattered light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an imaging apparatus, according to anembodiment.

FIG. 2 is a diagram showing an example of light scattered and reflectedafter impinging upon a clear polyethylene terephthalate (PET) filmcoated with scattering microparticles, according to an embodiment.

FIG. 3 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to an embodiment.

FIG. 4 is a two-dimensional (2-D) cross-section diagram showing anexpanded view of the diffusion light guide of FIG. 3.

FIG. 5 is a display of a substantially circular illumination beampattern formed at the exit window of the diffusion light guide of theimaging apparatus of FIG. 3.

FIG. 6 shows an example of the shape of the illumination beam formedpast the exit window of the diffusion light guide on a plane above thesurface of a film when an imaging apparatus is oriented vertically (90degrees) with respect to the surface of the film.

FIG. 7 shows an example of the shape of the illumination beam formedpast the exit window of the diffusion light guide on a plane above thesurface of the film (e.g., clean PET film in FIG. 2) when the imagingapparatus is oriented at an angle with respect to the surface of thefilm.

FIG. 8 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to another embodiment.

FIG. 9 is a two-dimensional (2-D) cross-section diagram showing anexpanded view of the diffusion light guide of FIG. 8.

FIG. 10 shows a substantially circular (semi-annular) illumination beampattern formed at the exit window of the segmented diffusion light guideof the imaging apparatus of FIG. 7.

FIGS. 11A-C are two-dimensional (2-D) cross-section diagrams of animaging apparatus, according to different embodiments.

FIG. 11D is an example of a dark-field image of the scatteringmicroparticles obtained by an imaging apparatus, according to anembodiment.

FIG. 12 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to yet another embodiment.

DETAILED DESCRIPTION

In some embodiments, an apparatus includes a housing and an image sensorthat is coupled to the housing and that has a field of view. Theapparatus also includes a non-imaging optical system coupled to thehousing and disposed outside of the field of view of the image sensor.The non-imaging optical system can output diffuse light in a set ofdirections to a surface to produce scattered light. The image sensor andthe non-imaging optical system are collectively configured such thatduring operation, the image sensor receives at least a portion of thescattered light.

In some embodiments, an apparatus includes a housing and an image sensorcoupled to the housing and having a field of view. The apparatus alsoincludes a non-imaging optical system coupled to the housing anddisposed outside of the field of view of the image sensor. Thenon-imaging optical system can output diffuse light in a set ofdirections from at least a first location and a second location of adistal end portion of the non-imaging optical system. The apparatusincludes at least a portion of the field of view of the image sensorbetween the first location and the second location. The image sensor canreceive from the surface at least one of a scattered light componentassociated with the first location or a scattered light componentassociated with the second location.

In some embodiments, an apparatus includes a diffusion light guidecoupled to a stylus housing. The diffusion light guide includes aproximal end portion and a distal end portion. The diffusion light guidecan receive light at the proximal end portion from a light source. Thediffusion light guide can send diffuse light from the distal end portionto a surface to produce a scattered light component that is receivedwithin an aperture of the diffusion light guide.

As used in this specification, the singular forms “a,” “an” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, the term “an image sensor” is intended to mean asingle image sensor or multiple image sensors.

As used in this specification, the terms “housing” and “stylus housing”relate to, for example, the outer container or cover of an imagingapparatus that holds the optical, electronic and mechanical componentsof the imaging apparatus, and can be used interchangeably unless thecontext clearly dictates otherwise.

FIG. 1 is a block diagram of an imaging apparatus, according to anembodiment. The imaging apparatus 100 includes a housing 110, an imagesensor 120 coupled to the housing 110 and having a field of view, and anon-imaging optical system 150 coupled to the housing 110. The housing110 can be made of, for example, plastic, steel, aluminum, etc. Thehousing 110 can be elongate and pen-shaped, and can include one or moreparts that can carry or enclose other parts of the imaging apparatus 100such as, for example, a battery (not shown in FIG. 1). Each of thecompartments of the housing 110 can be accessible via a fully orsemi-detachable lid. The housing 110 can also define one or more spacesfor one or more printed circuit boards (PCB) that can contain theelectronics for determining the accurate position information associatedwith the imaging apparatus 100. The housing 110 can define a firstopening through which images can be captured by the image sensor 120 anda second opening through which a stylus (not shown in FIG. 1) of thewriting tip can protrude or extend.

The image sensor 120 is coupled to and/or disposed within the housing110 of the imaging apparatus 100 and has a field of view (FOV). In someconfigurations, the image sensor 120 and the non-imaging optical system150 can be collectively set up or configured such that the image sensor120 can receive at least a portion of the light scattered and reflectedfrom a surface (e.g., a film) after being illuminated by the non-imagingoptical system 150. The image sensor 120 can detect the power of thescattered light and the power of the specular reflected light. The imagesensor 120 can be arranged to define an object plane and an image plane,where an object that is located in a field of view in the object planeis reproduced as an image in the image plane. The image sensor 120 canalso include a photo-detector that is substantially co-located with theimage plane to physically or electronically capture the image. Such aphoto-detector can be, for example, a Image Dissector Tube, a chargecoupled device (CCD) camera, a photodiode array detector, a pixel arraydetector, an avalanche photodiode (APD), and/or the like. In someconfigurations, the image sensor 120 and the non-imaging optical system150 can be collectively configured such that, during operation of theimaging apparatus 100, the image sensor 120 receives at least a portionof the received scattered light and at least a portion of the specularreflected light component, but the magnitude of the received scatteredlight is less than the magnitude of the portion of the received specularreflected light.

In the imaging apparatus 100 shown in FIG. 1, the illumination pathwayis the path taken by the illumination light propagating from a lightsource (of the non-imaging optical system 150) via one or multipleoptical, electrical and/or mechanical components to impinge upon thetarget (e.g., a surface of a film). The imaging pathway is the pathtaken by the scattered light propagating from the scatteringmicroparticles (located within a film) via one or multiple optical,electrical and/or mechanical components to the imaging sensor 120. Afterdetecting the power of the scattered and/or specular reflected light,the image sensor 130 can send an output voltage to, for example, acontrol module (not shown in FIG. 1). In some configurations, the imagesensor 120 can include optional beam shaping/collection lenses that canenhance the efficiency of scattered light collection. In yet otherconfigurations, the image sensor 130 can include two or morephoto-detectors to establish multiple imaging pathways.

The non-imaging optical system 150 can include light sources such as,for example, light emitting diodes (LEDs), organic light emitting diodes(OLEDs), semiconductor lasers, and/or the like. Additionally, thenon-imaging optical system 150 can also include optical lenses and/orprisms to efficiently deliver the illumination light to the targetsurface and include electronic or mechanical optical shutters to selectthe optimal image path. In some configurations, the non-imaging opticalsystem 150 can also include a diffusion light guide that has a proximalend portion and a distal end portion. The diffusion light guide can beoperatively coupled to the light source and configured to send thediffuse light from the distal end portion of the diffusion light guidefrom at least a first location and a second location where a portion ofthe field of view is between the first location and the second location.In other configurations, the non-imaging optical system includes a lightsource and a diffusion light guide having a distal end portion, aremaining portion, an inner surface and an outer surface. The lightsource contained within the non-imaging optical system 150 can outputlight having a range of wavelengths and the diffusion light guide canreceive the light from the light source and can send the diffuse lightfrom the distal end portion of the diffusion light guide. In suchconfigurations, the inner surface of the remaining portion of thediffusion light guide can be an absorptive surface at the range ofwavelengths; the outer surface of the diffusion light guide can be areflective surface at the range of wavelengths.

In other configurations, the non-imaging optical system 150 can includea light source and a diffusion light guide having a distal end portionand a remaining portion. In such configurations, the diffusion lightguide can be operatively coupled to the light source and configured tosend the diffuse light from the distal end portion of the diffusionlight guide in a substantially circular pattern, while the field of viewalong the remaining portion of the diffusion light guide can besubstantially surrounded by the remaining portion of the diffusion lightguide.

In yet other configurations, the non-imaging optical system 150 caninclude a first light source, a second light source, a segmenteddiffusion light guide that defines a first diffusion light guide and asecond diffusion light guide. In such configurations, the firstdiffusion light guide can have a distal end portion and a remainingportion, and the second diffusion light guide can have a distal endportion and a remaining portion. In such configurations, the firstdiffusion light guide can be operatively coupled to the first lightsource and configured to send a portion of the diffuse light from thedistal end portion of the first diffusion light guide in a firstsubstantially arcuate pattern. In such configurations, the seconddiffusion light guide can be operatively coupled to the second lightsource and configured to send a portion of the diffuse light from adistal end portion of the second diffusion light guide in a secondsubstantially arcuate pattern. The first substantially arcuate patternand the second substantially arcuate pattern can collectively define asubstantially circular pattern. In such configurations, the field ofview collectively along the remaining portion of the first diffusionlight guide and the remaining portion of the second diffusion lightguide can be substantially surrounded by the remaining portion of thefirst diffusion light guide and the remaining portion of the seconddiffusion light guide.

Furthermore, in other configurations, the non-imaging optical system 150can be a first non-imaging optical system. In such configurations, theimage sensor 130 and the first non-imaging optical system 150 can becollectively configured such that the image sensor 130, duringoperation, does not receive a specular reflected light componentassociated with a first location and a specular reflected lightcomponent associated with a second location. In such configurations, theimaging apparatus 100 can include a second non-imaging optical systemcoupled to and/or disposed within the housing 110 and configured tooutput light to the surface to produce a specular reflected lightcomponent. In such configurations, the image sensor 130 and the secondnon-imaging optical system can be collectively configured such that,during operation, the image sensor 130 receives at least a portion ofthe specular reflected light component output by the second non-imagingoptical system.

FIG. 2 is a diagram showing an example of light scattered and reflectedafter impinging the surface of a clear polyethylene terephthalate (PET)film coated with scattering microparticles, according to an embodiment.The incident illumination 202 impinges upon the surface of the clear PETfilm 204 at an angle of incidence (θ_(i)) with respect to the surfacenormal 206. The scattering microparticles are translucent and hence asignificant amount of the incident illumination passes through the clearPET film 204. Hence, approximately 50-75% of the incident illuminationis transmitted through the clear PET film as the transmitted light 208as shown in FIG. 2. The scattering of the illumination light by thescattering microparticles present on the surface of the clear PET film204 can be dependent on a number of parameters such as, for example, theloading density of the scattering microparticles 210, the size of thescattering microparticles 210, the shape of the scatteringmicroparticles 210, the material used in the scattering microparticle210 fabrication, the propensity of the scattering microparticles 210 toform aggregates and other higher order structures, etc. Hence, the exactdistribution of scattered light 212 in some cases can be isotropic innature.

Many applications based on optical detection assume perfect diffusereflections and assume specular reflections to be an outlier phenomenon.In reality, however, the presence of specular reflections is inevitable.Hence, incorporating the knowledge of specular reflections is desirableto make the optical detection methods robust. For a perfectly flat andsmooth surface (i.e., a perfect mirror), the direction of specularreflection 216 follows the law of reflection, which states the angle ofincoming illumination θ_(i) and the angle of outgoing reflected lightare the same (θ_(i)=θ_(r)). In many surfaces that are not perfectmirrors, however, a certain degree of specularity can also be observedeven though the direction of reflection θ_(r) is not identical to thedirection of incidence θ_(i). In other words, specular reflections donot only form a sharp line (spike) distribution of reflection, but canalso form a lobe distribution. Therefore, specular reflections can formtwo components: (1) specular spike and (2) specular lobe 216, which isillustrated in FIG. 2. The size and shape of the lobe of the specularreflected light 216 can depend on the size and the granularity ofsurface imperfections. Additionally, the specular reflection lobe 216width is also dependent on the nature of the surface roughness and scaleof the surface roughness compared to the incident light wavelength.

FIG. 3 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to an embodiment. The imaging apparatus 300produces a single diffuse light ring illumination towards the targetsurface. The imaging apparatus 300 includes a housing 310, an imagesensor 320, an LED 330, a stylus 335, a diffusion light guide 312 thatdefines an exit window 314 and has an external reflective surface 316and an internal absorbing surface 318. The diffusion light guide 312 hasa distal portion 370 as denoted by the bold dotted arrow in FIG. 3 and aremaining portion 372 (see FIG. 4) that is between the distal endportion 370 and a proximal end portion 374 (also denoted by a bolddotted arrow) and includes the proximal end portion 374. The proximalend portion 374, the distal end portion and 370 the remaining portion372 of the diffusion light guide 312 can also be seen in the expandedview of the diffusion light guide 312 shown in FIG. 4. The diffusionlight guide 312 is operatively coupled to the LED 330 and can send thediffuse light of a single wavelength or a range of wavelengths from theexit window 314 of the diffusion light guide 312 in a substantiallycircular or annular pattern (as shown in FIG. 5 and discussed furtherbelow).

Note that FIG. 3 is a 2-D cross sectional diagram of the imagingapparatus 300. In 3-dimensions (3-D), the diffusion light guide 312 cansubstantially be a two-layered cylindrical structure. The two-layeredcylindrical structure can include an external layer 312 a and aninternal layer 312 b. The external layer can be composed of, forexample, a solid plastic, metallic or polymer material that is coatedwith the reflective surface 316. The external layer 312 a is tapered andbeveled at the distal end portion to concentrate the illumination lightat the exit window 314 (see FIG. 4). The internal layer 312 b can be aconical structure that can be composed of, for example, glass or anyother polymer material that is transparent to light in the range ofwavelengths used in the imaging apparatus 300. Alternatively, internallayer 312 b can be air.

The field of view of the image sensor 320 along the remaining portion ofthe diffusion light guide 312 is substantially surrounded by theremaining portion of the diffusion light guide 312. The diffusion lightguide 312 is coupled to the housing (or stylus housing) 310 and canreceive light at the proximal end portion of the diffusion light guide374 from the light source (e.g., LED 330) and send diffuse light fromthe distal end portion of the diffusion light guide 370 to the (target)surface to produce a scattered light component (from the scatteringmicroparticles). The scattered light component is received within thedistal end portion aperture 336 of the internal layer 312 b of thediffusion light guide (see FIG. 4). The diffusion light guide 312 isoperatively coupled to the image sensor 320 and during operation, thereceived scattered light travels through the diffusion light guide 312and impinges upon the image sensor 320 via the proximal end portionaperture 337 of the internal layer 312 b of the diffusion light guide(see FIG. 4).

The diffusion light guide 312 is tapered to concentrate the light at theexit window 314 (see FIG. 4). Additionally, the exit window 314 is alsobeveled to direct the illumination light into the imaging zone 313 (seeFIG. 4). The (optional) reflective coating 316 on the external surfaceof the diffusion light guide 312 improves the optical efficiency for oneor a range of illumination wavelengths. Note that the internal surfaceof the external layer 312 a of the diffusion light guide 312 has twodistinct portions 318 and 319 (see FIG. 4). The inner portion of theinternal surface 319 that faces the incident illumination light has areflective coating to reflect the incident illumination light. The outerportion of the internal surface 318 has an absorptive coating to preventreflections of the incident illumination light from striking thephoto-detector or imaging lens of the image sensor 320. In someconfigurations, additional focusing and/or beaming lenses and otheroptical components (e.g., Fresnel prisms) can be added for increaseddelivery of the illumination light and/or increased collection of thescattered light and/or increased rejection of the specular reflectedlight.

FIG. 5 is a display of a substantially circular illumination beampattern formed at the exit window of the diffusion light guide of theimaging apparatus of FIG. 3. In some instances, the profile of theillumination beam can spread out laterally (i.e., along the x and yaxes) by the time the illumination beam is incident on the upper surfaceof the film (e.g., clean PET film in FIG. 2) due to, for example, theeffects of scattering (from the air particles) and/or other diffusioneffects. Hence, in such instances, the illumination light pattern formedat the surface of the film may not appear to be as substantiallycircular as the image presented in FIG. 5 and instead may appear to bespread out (or smeared). In other instances, the effects of scatteringand/or diffusion may not be isotropic and hence the amount of scatteringand/or diffusion of the incident illumination beam along the x-axis canbe either greater or lower than that of the scattering and/or diffusionalong the y-axis. In such instances, the profile of the illuminationbeam at the upper surface of the film may be substantially oval in shape(instead of being substantially circular as shown in FIG. 5).

FIG. 6 shows an example of the shape of the illumination beam formedpast the exit window of the diffusion light guide on a plane above thesurface of the film (e.g., clean PET film in FIG. 2) when the imagingapparatus is oriented vertically (90 degrees) with respect to thesurface of the film. FIG. 6 shows that in the vertical orientation, theillumination beam forms a substantially circular pattern on a planeabove the film. Additionally, the field of view of the imaging apparatusis contained within with the circular (annular) ring. It is expectedthat at least a portion of the illumination ring is within the field ofview of the imaging apparatus for the illumination light to impinge uponthe scattering microparticles in the field of view of the imagingapparatus. In some instances, the scattering of the illumination beam(by the air particles) upon exiting the exit window of the diffusionlight guide and/or other optical effects can lead to spreading orsmearing of the illumination beam as it strikes the surface of the film.This can lead to a larger portion of the circular (or annular)illumination beam profile being with the field of view of the imagingapparatus and may have the advantageous effect of increasing thesensitivity of the imaging apparatus.

FIG. 7 shows an example of the shape of the illumination beam formedpast the exit window of the diffusion light guide on a plane above thesurface of the film (e.g., clean PET film in FIG. 2) when the imagingapparatus is oriented at an angle with respect to the surface of thefilm. FIG. 7 shows that due to the tilted orientation of the housing 410(of the imaging apparatus 400) with respect to the surface of the film460, the illumination beam shape formed at the surface of the film 460is oval in shape and additionally, is non-uniform in width andintensity. The change in shape of the beam shape from beingsubstantially circular (e.g., for the vertical orientation of theimaging apparatus as shown in FIG. 6) being substantially oval is due tothe tilt of the housing 410 with respect to the film 460. Hence, thelight exiting the exit window of the diffusion light guide from thedistant end 461 (i.e., the end that is higher or further away from thesurface of the film 460) travels a longer distance than the lightexiting the exit window of the diffusion light guide from the closer end462 (i.e., the end that is lower or closer to the surface of the film460). As a result, the illumination light from the distant end 461 ofthe imaging apparatus 400 strikes the surface of the film 460 at alocation that is further away from the optical axis compared to thelocation where the light from the closer end 462 of the imagingapparatus guide strikes the surface of the film 460. Hence, theincreased distance traveled by the illumination beam from one end of theimaging apparatus 400 leads to the oval shape of the illumination beamprofile. Additionally, the illumination beam profile is non-uniform inwidth and intensity also because of the tilt of the housing 410 withrespect to the surface of the film 460. The increased distance traveledby the illumination light from the distant end 461 of the imagingapparatus 400 leads to increased scattering by the air particles and canalso involve additional optical effects. Hence, the intensity of theillumination light from the distant end 461 is lower when compared tothe intensity of the illumination light striking the film from thecloser end 462 of the imaging apparatus 400. As a result, theillumination light from the distant end 461 of the imaging apparatus 400gets progressively lower in intensity and width the further the distancethe illumination light has to travel before striking the surface of thefilm 460 (i.e., the further the distance traveled, the lower theillumination light intensity and width).

FIG. 7 shows that the profile of the illumination light on the uppersurface of the film 460 is dependent on the distance and the orientationof the imaging apparatus 400 with respect to the film 460. Under certainorientations of the imaging apparatus 400, specular reflection canreflect back into the field of view of the image sensor of the imagingapparatus. Because the specular reflected light is typically of greaterintensity than the scattered light (from the scattering microparticles),the specular reflected light can dominate the image if the specularreflected light is in the field of view of the image sensor. This cansignificantly reduce the contrast (and signal-noise-ratio) of the imagesformed on the image sensor. The amount of specular reflection receivedby the image sensor can depend on several parameters such as, forexample, the field of view of the image sensor, the tilt of the imagingapparatus with respect to the surface of the film, the orientation ofthe light source with respect to the optical axis of the image sensor,the presence of collimating and/or focusing lenses in both theillumination pathway and the imaging pathway, and/or the like. Thespecular reflected light can be prevented from reaching the image sensorif the angle of incidence and reflection (that includes the entirespecular lobe) can be made to lie outside the field of view of the imagesensor. Thus, in some instances, depending on the particularconstruction, the imaging apparatus 400 can be designed to avoidspecular reflections caused by tilt angles that naturally result fromeither left-handed or right-handed users.

FIG. 8 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to another embodiment. The imaging apparatus 500produces multiple diffuse light ring illuminations on the targetsurface. A detailed diagram of the two-dimensional(2-D) cross-section ofthe segmented diffusion light guide 512 in FIG. 8 is shown in FIG. 9.Note that each part of the segmented diffusion light guide 512 as shownin FIG. 9 has two distinct internal surfaces 518 a and 519 a. The innerportion of the internal surface 519 a that faces the incidentillumination light can have a reflective coating to reflect the incidentillumination light. The outer portion of the internal surface 518 a canhave an absorptive coating to prevent reflections of the incidentillumination light from striking the photo-detector or imaging lens ofthe image sensor 520.

Referring to FIGS. 8 and 9, the imaging apparatus 500 includes a housing510, an image sensor 520, a first LED 530, a second LED 532, a segmenteddiffusion light guide 512. The segmented diffusion light guide 512defines a first diffusion light guide 512 a and a second diffusion lightguide 512 b, where each diffusion light guide defines an exit window 514a or 514 b and has an external reflective surface 516 a or 516 b and aninternal absorbing surface 518 a or 518 b. The first diffusion lightguide 512 a has a distal end portion 570 a and a remaining portion 572a, and the second diffusion light guide 512 b has a distal end portionand a remaining portion (not marked in FIG. 9).

In FIGS. 8 and 9, the non-imaging optical system of the imagingapparatus 500 includes the first LED 530, the second LED 532, a firstdiffusion light guide 512 a and a second diffusion light guide 512 b(that collectively forms the segmented diffusion light guide 512). Thefirst diffusion light guide 512 a is operatively coupled to the firstLED 532 and can send a portion of the diffuse light from the distal endportion of the first diffusion light guide 570 a in a firstsubstantially arcuate pattern. The second diffusion light guide 512 b isoperatively coupled to the second LED 530 and can send a portion of thediffuse light from the distal end portion of the second diffusion lightguide in a second substantially arcuate pattern such that the firstsubstantially arcuate pattern and the second substantially arcuatepattern collectively define a substantially circular (or annular)pattern. The field of view of the imaging apparatus 500 collectivelyalong the remaining portion of the first diffusion light guide 572 a andthe remaining portion of the second diffusion light guide issubstantially surrounded by the remaining portion of the first diffusionlight guide 572 a and the remaining portion of the second diffusionlight guide.

The non-imaging optical system of the imaging apparatus 500 can outputdiffuse light in a set of directions from at least a first location ofthe distal end portion of the non-imaging optical system 562 a (see FIG.8) and a second location of the distal end portion of the non-imagingoptical system 562 b (see FIG. 8), where at least a portion of the fieldof view is between the first location 562 a and the second location 562b. The image sensor 520 can receive from a surface of the film at leastone of (1) a scattered light component associated with the firstlocation 562 a, or (2) a scattered light component associated with thesecond location 562 b. In some configurations, an electrical ormechanical controller (not shown in FIGS. 8 and 9) can be used toselectively activate at least one of the first LED 530 or the second LED532 based on an orientation of the housing 510 relative to the uppersurface of the film.

As discussed above, illumination light from each of the LEDs 530 and 532is received by each of the segments of the segmented diffusion lightguide 512 a and 512 b. The segmented diffusion-light-guide 512 of theimaging apparatus 500 produces or outputs a semi-annular illuminationgeometry when both the diffusion light guide segments receiveillumination from each of the LEDs 530 and 532 (as shown in FIG. 10).FIGS. 8 and 9 show the segmented diffusion light guide 512 having twosegments as a way of example only, and not by limitation. In otherconfigurations, the segmented diffusion light guide 512 can include morethan two segments that are either radially symmetrical or radiallynon-symmetrical. Hence, in other configurations, the imaging apparatus500 can also include more than two LEDs as light sources. Additionally,the LED light sources 530 and 532 can be controlled to operateindependently or in defined combinations. Each of the segments of thesegmented diffusion light guide 512 can be tapered to concentrate theillumination light at the exit window and each exit window can bebeveled to direct the illumination light at targeted imaging zone 513.The (optional) reflective coating 516 a and 516 b on the externalsurface of each segment of the segmented diffusion light guide 512improves the optical efficiency for one or a range of wavelengths of thereceived illumination light. The internal surface of each segment of thesegmented diffusion light guide 512 can be coated with an absorbingcoating 518 a and 518 b to minimize or reduce reflections and scattering(for one or a range of incident illumination wavelengths) into the imagesensor 520. In some configurations, additional focusing and/or beaminglenses and other optical components (e.g., Fresnel prisms) can be addedfor increased delivery of the incoming light via the illuminationpathways and/or increased collection of the scattered light and/orincreased rejection of the specular reflected light via the imagingpathway.

An advantage of using the embodiment of the imaging apparatus shown inFIGS. 8 and 9 for detecting the location of the distal end portion ofthe imaging apparatus 500 with respect to the upper surface of the filmis that either of the light sources (e.g., LEDs 530 or 532) can bechosen to illuminate their respective diffusion light guides 512 a or512 b based on the orientation of the housing 510 relative to the uppersurface of the film. Additionally, the multiple light ringconfigurations can also be selectively illuminated to avoid or reducethe specular reflection from reflecting back into and being received bythe image sensor 520 while the imaging apparatus 500 is held at a tiltangle (i.e., non-zero angle) with respect to the surface of the film.This is because at a specific non-zero tilt angle, the light output fromthe two or multiple segments of diffusion light guide 512 will havevarying angle of incidences with respect to the surface normal. As aresult, the light output from a light source(s) can be selected suchthat the specular reflectance lobe is out of or substantially out of thefield view of the image sensor 520. This can significantly increase thesensitivity of the imaging apparatus and improve the precision fordetection of the location of the imaging apparatus.

FIG. 10 is the substantially circular (semi-annular) illumination beampattern formed at the exit window of the segmented diffusion light guideof the imaging apparatus of FIG. 8. FIG. 10 shows two breaks (marked asA and A′ in FIG. 10) in the continuity of the circular (or annular)pattern of the illumination beam profile. These break points correspondto the locations where the diffusion light guide has been segmented.Because FIG. 10 shows the diffusion light guide having two segments, twobreak points exist in the illumination light beam profile. In otherconfigurations, the diffusion light guide can have more than twosegments that are either radially symmetrical or radiallynon-symmetrical. In such configurations, the illumination beam profilecan also have more than two break points that are either radiallysymmetrical or radially non-symmetrical. In some instances, the profileof the illumination beam can spread out laterally (i.e. along the x andy axes) by the time the illumination beams strikes the upper surface ofthe film (e.g., clean PET film in FIG. 2) due to the effects ofscattering (from the air particles) and/or other optical effects. Hence,in such instances, the illumination beam pattern formed at the uppersurface of the film may not appear to be as substantially circular(semi-annular) as the image presented in FIG. 10 and instead may appearto be spread out (or smeared). In other instances, the effects ofscattering may not be isotropic and hence the amount of scattering ofthe incident illumination beam along the x-axis can be either greater orlower than that of the scattering along the y-axis. In such instances,the profile of the illumination beam at the upper surface of the filmmay be substantially oval in shape (with one or multiple break points)instead of being substantially circular (semi-annular) as shown in FIG.10.

Although FIGS. 1-10 described two separate embodiments of the imagingapparatus that were based on a dark field single ring configuration or adark field multiple ring configuration, alternative embodiments of theimaging apparatus are possible. FIG. 11 summarizes some examples ofpossible embodiments. FIG. 11A shows a 2D cross-sectional image of animaging apparatus 600 in the dark field single ring configuration. Theimaging apparatus 600 includes a housing 610, an image sensor 620, alight source 630 (e.g., LED), and a diffusion light guide 612. A film660 contains the scattering microparticles. Operation of the imagingapparatus 600 shown in FIG. 11A is similar to the operation of theimaging apparatus 300 discussed in FIG. 3. FIG. 11B shows a 2Dcross-sectional image of an imaging apparatus 600 in the dark fieldmultiple rings configuration. The imaging apparatus 600 shown in FIG.11B includes a housing 610, an image sensor 620, light sources 630 and632 (e.g., LED's), and a (segmented) diffusion light guide 612. A film660 contains the scattering microparticles. Operation of the imagingapparatus 600 shown in FIG. 11B is similar to the operation of theimaging apparatus 500 discussed in FIG. 8.

FIG. 11C shows a 2D cross-sectional image of an imaging apparatus 600,according to another embodiment. The imaging apparatus 600 shown in FIG.11C includes a housing 610, an image sensor 620, light sources 630, 632and 633 (e.g., LED's), a diffusion light guide 612, and a light guidingstylus 635. A film 660 contains the scattering microparticles. In suchembodiments, the imaging system 600 can include an a primaryillumination (light) source as defined by the LEDs 630 and 632 and thediffusion light guide 612, and an alternative illumination (light)source as defined by the LED 633 and the light guiding stylus 635.

The various embodiments of the imaging apparatus shown in FIGS.3-11(A-C) can operate either in the dark-field imaging mode or thebright-field imaging mode. In such embodiments, a control modulecontained within the imaging apparatus that can implement signalprocessing functionalities can select a particular imaging modality(i.e., bright-field imaging or dark field-imaging) based on theinstantaneous or near-instantaneous imaging conditions as described ingreater detail herein. The control module can adapt to either abright-field or dark-field imaging situation that depends on theinstantaneous geometrical orientation between the stylus and the surfaceof the film. Note that in such cases, it is not compulsory to have twoor more or more non-imaging (illumination) sources, although more thanone illumination source can be acceptable. Thus, any of the embodimentsdisclosed in FIGS. 3-11(A-C) can operate in the light-filed ordark-field imaging mode if equipped with the appropriate signalprocessing functionality, and in such cases, the secondary non-imagingillumination source may optionally be omitted.

A control module (not shown in FIGS. 3-11(C)) that can implement signalprocessing functionalities and is associated with real time or near-realtime image processing can select the imaging modality (i.e., eitherbright-field or dark-field) that is activated based on the instantaneousor near-instantaneous imaging conditions. The control module can be, forexample, a hardware module and/or software module stored in a memoryand/or executed in a processor on the printed circuit boards (PCB) ofthe imaging apparatus. For the dark-field image, providing satisfactoryexclusion of specular reflection can be achieved and the appropriateimage processing methods can be applied by the control module. Asdescribed in greater detail herein, the background of the finaldark-field image formed at the image sensor will be dark and scatteredlight from the scattering microparticles will form white dots or spots.For the bright-field image, it is desirable to capture the specularreflected light. Hence, the background of the bright-field image formedon the image sensor will be bright while the location of the scatteringmicroparticles will comparatively darker than the background due thesubstantially isotropic or substantially semi-isotropic scattering ofthe incident illumination by the scattering microparticles. Based on thequality of both the dark-field and bright-field image formed on theimage sensor, the control module can select the proper method fordetecting light spots on a dark background (dark-field imaging) or darkspots on a light background (bright-field imaging). Thus the imagingapparatus can implement a single imaging pathway for operation becauseat any given time, the imaging apparatus is operating in either thedark-field imaging mode or the bright-field imaging mode. In thisembodiment, the optical, imaging and illumination systems remainconstant and the image processing methods adapt to the current modality.

When producing the dark-field image, the specular reflected light iseither prevented from striking (or being detected by) the image sensor(e.g., image sensor 620 in FIG. 11) or the amount of specular reflectedstriking (or being detected by) the image sensor is minimized orreduced. Hence, the background of the dark-field image that is formed onthe image sensor is dark. The bright spots on the dark-field imageappear from the scattered reflection from the scattering microparticles.FIG. 11D shows an example of such a dark-field image. When producing thebright-field image, the specular reflected light is allowed to strike(or be detected by) the image sensor. Hence, the background of thebright-field image that is formed on the image sensor is bright. Thedark spots on the bright-field image appear from the scatteringmicroparticles because the scattered reflection (which can be isotropic)from the microparticles reduces the intensity of light reaching thefield of view of the image sensor. Hence, light scattered bymicroparticles appear within an image as comparatively dark with respectto the background.

FIG. 12 is a two-dimensional (2-D) cross-section diagram of an imagingapparatus, according to yet another embodiment. In such embodiments, theimaging apparatus illustrates the use of beam steering components and anasymmetric distribution of the non-imaging (illumination) light sources.The imaging apparatus 700 can include an image sensor 720 coupled to ordisposed within a housing 710 and having a field of view. The imagingapparatus 700 can include a first non-imaging optical system coupled tothe housing 710 that includes a first light source (e.g., LED 730) and afirst set of beam steering optical elements (e.g., prism 725) coupled tothe housing 710. In such embodiments, the first non-imaging opticalsystem can output (either diffuse or non-diffuse) light in multipledirections from at least a first location 764 and a second location 765(or multiple locations) of the first non-imaging optical system toproduce the (either diffuse or non-diffuse) light illumination pathway780. The image sensor 720 can receive from a surface of the film atleast one of (1) a scattered light component associated with the firstlocation, or (2) a scattered light component associated with the secondlocation. In such embodiments, the image sensor 720 and the firstnon-imaging optical system can be configured such that the image sensor720, during operation, does not receive a specular reflected lightcomponent associated with the first location and a specular reflectedlight component associated with the second location to form an optimaldark-field image on the image sensor 720.

The imaging apparatus 700 can also include a second non-imaging opticalsystem coupled to the housing 710 that includes a second light source(e.g., LED 732) and, optionally, a second set of optical elements (notshown in FIG. 12) coupled to or disposed within the housing 710. Thesecond non-imaging optical system can output light to the surface of thefilm to produce the light illumination pathway 782 that produces aspecular reflected light component and/or a scattered light componentfrom the scattering microparticles on the surface of the film. In someinstances, the image sensor 720 and the second non-imaging opticalsystem can be collectively configured such that, during operation, theimage sensor 720 receives at least a portion of the specular reflectedlight component output by the surface of the film after being impingedupon by the illumination light from the light illumination pathway 782.In other instances, the image sensor 720 and the second non-imagingoptical system can be collectively configured such that, duringoperation, the image sensor 720 receives at least a portion of thescattered light component from the scattering microparticles on thesurface of the film and does not receive a specular reflected lightcomponent.

Note that the angle of incidence of the first light illumination pathway780 is not equal to the angle of incidence of the second first lightillumination pathway 782. One or more beam steering optical elements(e.g., prism 725) can be used to vary the angle of incidence of thelight illumination pathway (either illumination pathway 780 orillumination pathway 782) to account for topographical variations as thestylus 735 moves over the surface of the film due to, for example,manufacturing imperfections, changes in the user's positioning of thestylus 735, etc. These topographical variations can lead to changes inthe angle of the scattered light (from the scattering microparticles)with respect to the image sensor 720. Additionally, the asymmetricdistribution of the (non-imaging) light illumination pathways can allowone of the light illumination pathways (either illumination pathway 780or illumination pathway 782) to be more suitable to illuminate thesurface of the film according to different orientations of the stylus735 with respect to the film. As described above, the embodiment of theimaging apparatus 700 can also be operated in either the dark-fieldimaging mode or the bright-field imaging mode if a control module can beincluded in the imaging apparatus 700 that can implement specific signalprocessing functionalities.

The embodiments of the imaging apparatus discussed in FIGS. 1-12 dealwith receiving (or rejecting) the specular reflected light and thescattered light from the scattering microparticles contained within thedisplay film. In other embodiments, however, the imaging apparatus caninvolve receiving a fluorescent signal generated by fluorescentmicroparticles embedded within the surface of the display film (insteadof scattering microparticles). In such embodiments, the microparticlesused can be transparent and can be impregnated with a fluorescentcompound that can be tuned to fluoresce at certain wavelengths. Oneexample can involve using fluorescent microparticle that can be excitedby the imaging apparatus at ultra-violet (UV) wavelengths and generatingfluorescence at infra-red (IR) wavelengths. The large Stokes shift(difference between the excitation wavelength and the emissionwavelength of the fluorescent microparticles) can be used to improve thesignal-noise ratio of the image formed at the image sensor of theimaging apparatus. In such embodiments, the imaging apparatus can beconfigured to respond to the IR fluorescence signal and reject allspecular reflected light in the UV range. The rejection of the specularreflected light and/or any bleedthrough of the excitation illuminationin the UV range can be implemented by using the appropriate emissionfilters in the imaging pathways. This configuration, however, caninvolve the addition of more optical components in the imaging apparatus(e.g., excitation filters, emission filters, etc.).

Any of the imaging apparatus described herein can include any suitableprocessor such that the generator and/or module performs the functionsdescribed herein. Such processors can be a general-purpose processor(e.g., a central processing unit (CPU)) or other processor configured toexecute one or more instructions stored in the memory. In someembodiments, the processor can alternatively be an application-specificintegrated circuit (ASIC) or a field programmable gate array (FPGA). Theprocessor can be configured to execute specific modules and/orsub-modules that can be, for example, hardware modules, software modulesstored in the memory and executed in the processor, and/or anycombination thereof. The memory included in the imaging apparatus canbe, for example, flash memory, one time programmable memory, a randomaccess memory (RAM), a memory buffer, a hard drive, a read-only memory(ROM), an erasable programmable read-only memory (EPROM), and/or soforth. In some embodiments, the memory includes a set of instructions tocause the processor to execute modules, processes and/or functions usedto generate, control, amplify, and/or transfer electric current toanother portion of the imaging apparatus.

Some embodiments described herein relate to a computer storage productwith a non-transitory computer-readable medium (also can be referred toas a non-transitory processor-readable medium) having instructions orcomputer code thereon for performing various computer-implementedoperations. The computer-readable medium (or processor-readable medium)is non-transitory in the sense that it does not include transitorypropagating signals per se (e.g., a propagating electromagnetic wavecarrying information on a transmission medium such as space or a cable).The media and computer code (also can be referred to as code) may bethose designed and constructed for the specific purpose or purposes.Examples of non-transitory computer-readable media include, but are notlimited to: magnetic storage media such as hard disks, floppy disks, andmagnetic tape; optical storage media such as Compact Disc/Digital VideoDiscs (CD/DVDs), Compact Disc-Read Only Memories (CD-ROMs), andholographic devices; magneto-optical storage media such as opticaldisks; carrier wave signal processing modules; and hardware devices thatare specially configured to store and execute program code, such asApplication-Specific Integrated Circuits (ASICs), Programmable LogicDevices (PLDs), Read-Only Memory (ROM) and Random-Access Memory (RAM)devices. Other embodiments described herein relate to a computer programproduct, which can include, for example, the instructions and/orcomputer code discussed herein.

Examples of computer code include, but are not limited to, micro-code ormicro-instructions, machine instructions, such as produced by acompiler, code used to produce a web service, and files containinghigher-level instructions that are executed by a computer using aninterpreter. For example, embodiments may be implemented using Java,C++, or other programming languages (e.g., object-oriented programminglanguages) and development tools. Additional examples of computer codeinclude, but are not limited to, control signals, encrypted code, andcompressed code.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Where methods and/or schematics described above indicatecertain events and/or flow patterns occurring in certain order, theordering of certain events and/or flow patterns may be modified.Additionally certain events may be performed concurrently in parallelprocesses when possible, as well as performed sequentially. While theembodiments have been particularly shown and described, it will beunderstood that various changes in form and details may be made.

Although various embodiments have been described as having particularfeatures and/or combinations of components, other embodiments arepossible having a combination of any features and/or components from anyof embodiments where appropriate. For example, any of the embodiments ofthe imaging apparatus described herein can include multiple lightsources, multiple imaging sensors with integrated control electronicsfor decoding the co-ordinates of the position-coding patterns on thedisplay surface, and transmitters for transmitting the positionco-ordinates to an external device.

What is claimed is:
 1. An apparatus, comprising: a stylus housing; anoptical radiation source coupled to the stylus housing and configured tooutput diffuse light in a plurality of directions from a stylus tipcoupled to the stylus housing to a surface to produce scattered light;an optical sensor configured to receive at least a portion of thescattered light and generate a signal indicating the portion of thescattered light received by the optical sensor; and a controllerconfigured to track a position of the stylus tip relative to the surfacebased, at least in part, on the signal; wherein: the optical radiationsource is configured such that a specular reflected light resulting fromreflection of the diffuse light off of the surface is outside of a fieldof view of the optical sensor; and the optical radiation sourcecomprises a first optical radiation source and a second opticalradiation source, and the controller is configured to activate one ofthe first optical radiation source or the second optical radiationsource based on an orientation of the stylus housing relative to thesurface to maintain the specular reflected light outside of the field ofview of the optical sensor.
 2. The apparatus of claim 1, wherein thesurface includes a touchscreen surface of a portable electronic device,and the controller is configured to control a communication deviceoperably coupled to the stylus housing to transmit informationindicating the tracked position of the stylus tip to the portableelectronic device.
 3. The apparatus of claim 1, wherein the opticalsensor comprises two or more photo-detectors.
 4. The apparatus of claim1, wherein the optical radiation source comprises one or more lightemitting diodes.
 5. The apparatus of claim 1, wherein the opticalradiation source comprises one or more semiconductor lasers.
 6. Theapparatus of claim 1, wherein the surface includes a clear film coatedwith scattering microparticles, and the scattered light is produced bythe diffuse light scattering against the scattering microparticles. 7.The apparatus of claim 1, wherein the diffuse light comprisesultraviolet radiation.
 8. The apparatus of claim 1, wherein the diffuselight comprises infrared radiation.
 9. A method of operating a stylusdevice, the method comprising: transmitting optical radiation fromwithin a stylus housing to a surface from a tip of the stylus device;receiving scattered light within the stylus housing through the tip ofthe stylus device, the scattered light including a portion of radiationscattered by the surface responsive to the optical radiation;determining a property of the scattered light received through the tip;tracking a location of the tip of the stylus device based, at least inpart, on the property of the scattered light received through the tip;wherein transmitting optical radiation from within the stylus housingcomprises: transmitting the optical radiation such that a specularreflected light resulting from reflection of the diffuse light off ofthe surface is outside of a field of view of an optical sensor receivingthe scattered light; and transmitting the optical radiation from a firstoptical radiation source and a second optical radiation source, andactivating, with a controller, one of the first optical radiation sourceor the second optical radiation source based on an orientation of thestylus housing relative to the surface to maintain the specularreflected light outside of the field of view of the optical sensor. 10.The method of claim 9, wherein the property of the scattered lightincludes a power of the scattered light received through the tip. 11.The method of claim 10, further comprising transmitting an outputvoltage indicating the power of the scattered light to the controller.12. The method of claim 9, further comprising applying a film coatedwith scattering micro-particles to the surface to improve scatteringcharacteristics of the surface.
 13. The method of claim 12, whereinapplying a film coated with scattering micro-particles to the surfaceincludes applying a clear polyethylene terephthalate (PET) film coatedwith the scattering micro-particles to the surface.
 14. The method ofclaim 12, wherein applying a film coated with scattering micro-particlesto the surface includes applying the film to a touchscreen display of aportable electronic device.
 15. The method of claim 9, whereintransmitting optical radiation from within a stylus housing to a surfacefrom a tip of the stylus device comprises transmitting one of infraredradiation or ultraviolet radiation from the tip of the stylus device.